In recent years, there has been a strong demand for a reduction of the amount of carbon dioxide emission for environmental protection. In the automobile industry, expectations have been attracted to the reduction of the amount of carbon dioxide emission caused by introduction of an electric vehicle (EV) or a hybrid electric vehicle (HEV), and the development of a secondary battery for motor driving, which serves as a key for practicalization of these, is being assiduously carried out. As the secondary battery, attention has been paid to a lithium ion battery which can achieve high energy density and high output density.
For increasing energy density of a lithium ion battery, attention has been paid to a silicon-based material (silicon, a silicon compound, and the like) having a larger theoretical capacity than a carbon material used as a negative electrode active material in the related art. However, in a case where the silicon-based material is used as the negative electrode active material, a volume change of the material in accordance with charging and discharging is large. Therefore, the silicon-based material itself is disintegrated due to the volume change or easily peeled off from the surface of a current collector, so that it was difficult to improve cycle characteristics.
Patent Literature 1 discloses a lithium ion battery in which expansion of a negative electrode is suppressed by adjusting a mixing ratio of carbon and at least one of silicon and a silicon compound and particle diameters thereof to a predetermined range.
Patent Literature 2 discloses a carbon material which contains carbon particles and fibrous carbon having a carbonaceous material containing Si and/or a Si compound deposited on at least a part of the surface of carbon particles having a graphite structure, the carbonaceous material being obtained by heat treating a composition containing a polymer. Further, an electrode paste containing the carbon material and a binder (binding agent) and an electrode containing the electrode paste are also disclosed.